1. Field of the Invention
The invention relates to internal combustion exhaust gas catalytic converters and more particularly to a method for allowing the direct coupling of a catalytic pre-converter to a monolithic honeycomb catalyst element.
2. Brief Description of the Related Art
Catalytic converters are the primary means used to control exhaust emissions from internal combustion engines. Catalytic converters, however, experience operational profiles where exhaust emissions control is limited or non-existent. One such operational profile occurs during cold engine start up, where one aspect limiting exhaust emissions control is insufficient heat in the catalytic converter to support catalytic combustion.
Numerous solutions have been proposed to this problem. These solutions can be broadly classed in three categories. The first is simply the more efficient use of the heat generated by the engine, whereby the catalytic converter is located as close as practicable to the engine exhaust manifold to minimize exhaust system heat loss prior to the exhaust gas entering the converter. The second group can be categorized as catalytic pre-heaters. This group is characterized by the use of an external energy source, such as electricity, to pre-heat the catalyst. The third and final group can be categorized as pre-converters. This group is categorized by the use of fast light-off pre-converters that can provide exothermic reactions using the limited existing heat within the exhaust gas.
The successful use of pre-converters depends upon being able to place the pre-converter in close proximity to both the exhaust manifold and the monolithic catalyst. It is critical that the pre-converter be able to exploit the limited heat of combustion coming from the engine as well as transmit most of the heat generated by its exothermic reaction to the monolithic catalyst. As a result of the former criteria, minimum sized catalytic converters with pre-converters have been desired due to the relative premium placed on space up around the engine's exhaust manifold. As a result of the latter criteria, it has been seen as desirable to co-locate the pre-converter and the monolithic catalyst. The greatest degree of co-location is currently accomplished by locating the pre-converter in an upstream piece of tailpipe coupled to the converter.
A short channel metal catalyst unlike other pre-converters allows for the pre-converter to be shaped to conform to the shape of the monolithic catalyst. A short channel metal catalyst, however, like other pre-converters requires an individualized mounting means, a means different than that used to mount the monolithic catalyst. Thus, there is a problem of co-locating a short channel metal catalyst pre-converter and a monolithic catalyst within a converter.